Residual Calculator

About this calculator

In regression and statistical modeling, a residual is the difference between what was actually observed and what a model predicted: residual = observed − predicted. This calculator also computes the absolute residual (its magnitude regardless of sign) and the percent residual (the residual as a percentage of the observed value), giving three views of the same gap in fit.

Statistics students, data analysts and researchers examine residuals to judge how well a regression line or model fits the data — plotting residuals against predicted values (a residual plot) reveals patterns a simple R² can hide, such as heteroscedasticity (residual spread growing with the predicted value) or nonlinearity (a curved pattern indicating a linear model is the wrong choice). A residual's sign also matters directly: a positive residual means the model underestimated that observation, a negative one means it overestimated it.